Justification:Ctenochaetus cyanocheilus is widely distributed and occasional to uncommon in most its range. It is caught incidentally in subsistence fisheries and for the aquarium trade but not at high levels. There are no major threats known. It is found in a number of marine reserves in parts of its distribution. It is therefore listed as Least Concern.

Ctenochaetus cyanocheilus is found from peninsular Malaysia, southern Sumatra and Vietnam to American Samoa and the Line Islands, north to Ogasawara Islands, Japan, south to the Great Barrier Reef, New Caledonia and Tonga (Randall and Clements 2001).

At Tuvalu, this species was six times more common than Ctenochaetus striatus (Randall and Clements 2001). It was recorded as occasional in terms of relative abundance in the northern Bismarck Sea, Papua New Guinea (Allen 2009). It is abundant in the American Samoa National Park (National Park of Samoa Checklist of Fishes, accessed 21 April 2010). It is occasional in the Philippines (R. Abesamis pers. comm. 2010). It is uncommon in the Marianas (R.F. Myers pers. comm. 2010).

The genus Ctenochaetus feed on fine detrital material. They whisk the sand or rocky substratum with their teeth and utilize suction to draw in the detrital material that consists of diatoms, small fragments of algae, organic material and fine inorganic sediment (Randall and Clements 2001). Species of Ctenochaetus share the presence of a thick-walled stomach (Randall and Clements 2001); this character is significant with respect to the nutritional ecology of this genus (Choat et al. 2002b). On the Great Barrier Reef, it is found in outer reef fronts below C. striatus (J.H. Choat pers. comm. 2010).

Surgeonfishes show varying degrees of habitat preference and utilization of coral reef habitats, with some species spending the majority of their life stages on coral reef while others primarily utilize seagrass beds, mangroves, algal beds, and /or rocky reefs. The majority of surgeonfishes are exclusively found on coral reef habitat, and of these, approximately 80% are experiencing a greater than 30% loss of coral reef area and degradation of coral reef habitat quality across their distributions. However, more research is needed to understand the long-term effects of coral reef habitat loss and degradation on these species' populations. Widespread coral reef loss and declining habitat conditions are particularly worrying for species that recruit into areas with live coral cover, especially as studies have shown that protection of pristine habitats facilitate the persistence of adult populations in species that have spatially separated adult and juvenile habitats (Comeros-Raynal et al. 2012).